Introduction: Breast cancer is the most prevalent cancer among women. In Germany, women are invited to a population-based mammography screening programme for the first time at the age of 50. Since it is still discussed whether the benefits of mammography screening outweigh its harms, the concept of informed choice has gained importance. The objective of this cross-sectional study is to assess the proportion of informed choices in the mammography screening programme. A special focus is on the examination of the impact of Turkish migration background and educational level on informed choices. Methods and analysis: The proportion of informed choices is evaluated in a cross-sectional study with 3-month follow-up for behavioural implementation of the screening intention. A randomly selected sample of 17 000 women aged 50 years living in Westphalia-Lippe, a region in the Federal State of North-Rhine Westphalia, is invited to participate in this study. To reach adequate numbers of Turkish women, all possibly Turkish women in the sample are identified through a name algorithm and contacted. The sample is drawn from women registered in the study area for which the registration offices consented to supply data for the study (88% of all towns/cities in the study region). Women identified through the Turkish name algorithm received all materials in German and Turkish. The primary outcome is informed choice. Data are collected on informed choice components (knowledge, attitude, decision/implementation) as well as on its possible determinants (eg, health behaviour, perceived behavioural control, subjective norms, invitation status, migration background and other demographic variables). Data are collected before the screening appointment and at 3 months follow-up. Ethics and dissemination: The study was approved by the ethical committee of the Medical Faculty of Muenster University. Results will be published in a relevant scientific journal and communicated to respondents and relevant institutions.